The present invention relates to a modified polyurethane, especially useful as a coating for athletic surfaces, that structionally incorporates a substantial quantity of silica into the polymer thereof and a method of manufacture of the composition.
Polyurethanes are utilized for coating many different types of surfaces, as foams, as elastomers and for numerous other purposes. While polyurethanes are useful for a wide variety of applications, they have been especially useful in coating athletic surfaces such as the floors of gymnasiums or basketball courts. For such purposes it is desirable for the polyurethane to have a low durometer yet a relatively high resilience, as the low durometer tends to cushion an impact made by an athlete on the surface and the high resilience tends to enhance the athletic performance of the athlete. In general it can be stated that athletic surfaces of this type preferably should have high elastomeric or dynamic properties.
Also in general terms, many different types of fillers can be and have been added to polyurethane precurser mixtures. The reason for adding fillers to conventional plastic materials has varied. For example, fillers may be added to increase bulk, to increase hardness, to increase thermal insulation or chemical resistance of a plastic such as polyurethane.
One of the fillers that has been conventionally used for this purpose has been silica (also referred to as sand or silicon dioxide). In particular, silica has been added to plastics to increase the hardness and thermal insulation characteristics of the plastics. While the silica is effective in improving certain qualities of plastics, it has always conventionally deteriorated other characteristics. In particular, when silica is added to polyurethane in a conventional manner, the polyurethane becomes more brittle and less elastomeric. For example, in the book Polyurethane: Chemistry and Technology; by Sanders et al, published by Wiley, NY in 1964 in Volume 1 page 343, a table indicates that elasticity of polyurethanes decreases as filler level is increased.
Since dynamic characteristics such as resilience are desirable for many of the uses of the polyurethane and, in particular, for uses of polyurethane on athletic surfaces, fillers such as silica have normally not been available for use in polyurethanes to be utilized for uses requiring good dynamic properties. Consequently, the amount of silica that has been added to conventional polyurethane coatings has been non existent or relatively small, when the coating requires good dynamic or elastomeric properties.
Because silica in the form of sand is a highly abundant, easily obtained and inexpensive building material, it is desirable to be able to incorporate silica into a polyurethane type of coating wherein the coating would maintain a relatively low durometer and not become brittle. Likewise, the coating should be relatively elastic or resilient and have generally overall good dynamic properties.
Because silica is so much less expensive in comparison to the other precurser components of a polyurethane, it is desirable that as much silica as possible also be utilized within the modified polyurethane. In order to accomplish this, a modified polyurethane is provided hereunder that structurally incorporates the silica into the modified polyurethane polymer rather than simply surrounding the silica or tethering the silica to the polyurethane polymer as in the prior art compositions.